Process for the manufacture of trialkylaluminium compounds



PROCESS FOR THE 'MANUFACTURE F TRIALKYLALUMINIUM COMPOUNDS Karl Ziegler and Konrad Nagel, Mulheim an der Ruhr, Germany; saidNagel assignor to said Ziegler No Drawing. Application May 12, 1953,

' Serial No. 354,626

Claims priority, application Germany May 13, 1952 4 Claims. "(CL 260-448) This invention relates to the manufacture of trialkylaluminium compounds. ferred to as aluminium trialkyls.

It is known that the so-called alkylaluminium sesquihalides, i. e. mixtures of alkylaluminium dihalides and dialkylaluminium monohalides,.can be produced from me- These compounds are alsore- ,7

tallic aluminium and alkyl halides as exemplified by the following equation: I

2Al+ 3C2H5Cl=AlCl2C2H5 +AlCl( CzHs 2 Substantially homogeneous dialkylaluminium monohalides may be produced by the'action of alkyl halides on I an alloy of 70% aluminium and %'magnesium according to Grosse and Mavity, Journal of Organic Chemistry (1940), 5, 110 and 119. This'alloy contains aluminium and magnesium approximately in the molar ratio equation:

2A1 +Mg+4RHal=2AlR2Hal+MgHal2 The formation of the aluminium trialkyls would appear to require the use of an aluminium-magnesium alloy which corresponds at least to the composition AlzMgs. Nothing has hitherto become known of any attempts to carry out the reaction AlzMgs 6RHal=3MgHala+ 2AlRs conditions of the Grignard reaction i. e. in solution'in ether. (E. Krause and B. Wendt, Berichte de Deutschen Chemischen Gesellschaft, 56, 466 (1923). Ether-free aluminium trialkyls alone are not obtained in this manner, as the ether cannot be removed from the etherates by simple means. Thus the problem of producing ether-free aluminium trialkyls directly from alkyl halides and suitable aluminium alloys (which would follow the known formation of tetraethyllead from PbNa4 and 4 molecules of ethyl chloride) has hitherto remained unsolved. The ether-free aluminium trialkyls have recently become important as polymerisation catalysts for olefins.

It has now been found that magnesium-aluminiumalloys having a composition in the region of 57-65% magnesium and 43-35% aluminium (Mg3Al2 to MgzAl) can, despite their high magnesium content, be reacted with alkyl halides in the absence of ether to yield only or mainly aluminium trialkyls. The alloys specified are extremely brittle and can, therefore, be powdered to a of 2:1, so that the reaction may be represented'bythe very fine dust without difiiculty. They are suitably added v in this form in the process of the invention. In addition Patented -May 1, 1956 -.matic hydrocarbons, but is best carried out direct with the alkyl halide in undiluted state. In the latter case, though, the demand on the stirring mechanism which has to be provided .in the reaction vessel is fairly heavy, since the reaction products contain a large quantity of magnesium halide and accordingly easily form solid lumps so that a too weak stirrer sticks. This difficulty may be overcome by working in a rotating drum which contains grinding bodies. The aluminium organic compounds produced are recovered from the solid or semisolid reaction mixtures by distillation or solvent extraction.

The first reaction products mostly still contain some halogen, e. g. the product from MgsAlz and ethyl bromide contains from 5 to 10%, and rarely up to 15 %,-of halogen which corresponds to a content-of about double this percentage of diethylaluminium bromide. This halogen contcnt may easily be removed by a further treatment with the very finely powdered aluminium-magnesium alloy at a temperature of ISO-170 C., whereupon pure, halogen-free aluminium trialkyls are obtained in high yields.

Example 1 1.3' kg. of finely powdered aIuminium magnesium alloy containing 40% Aland 60% Mg are mixed with "1 kg. ethylbromide in a small vessel furnished with a powerful stirring mechanism and an effective reflux cooler. After stirring for l-2.-hours,commencement of the reaction may be hastened by the addition of iodine or-rsome aluminium bromide or "ethylaluminiumsesquibromide"re-' action takes place with self-heating. A further'3.8 kg. of ethyl bromide is then added over a period of about 6 hours, intensive stirring being continued throughout. The stirring is continued so long as spontaneous reaction is noticeable (up to 24 hours). During this time the stirrer will occasionally stop. The mix may now be worked up by distilling oif the aluminium organic product which has formed. In this case a distillate is obtained which consists mainly of triethylaluminium, but which also contains 7-15 of bromine. It is better to heat the vessel, after spontaneous reaction has ceased, for 20 hours at C. and then to distill. In this manner a halogenfree distillate may be obtained directly. Yield: 1.2-1.4 kg.

triethylaluminium or about 70-85% of the theoretical yield.

Example 2 The procedure described in Example 1 is followed, but the reaction is carried out in a pressure-sealed reaction vessel, and instead of ethyl bromide a solution of 4 kg. of methyl bromide in 5 litres of hexane is used. After cessation of the spontaneous reaction, any of the following procedures may be followed: v

(a) A further 5 litres of hexane is added to the reaction 60 vessel and the mixture is stirred. After allowing settle- Thereupon the trimethylaluminium is distilled off in vacuo. Yield: 60-75 of the theoretical yield.

(b) The hexane is distilled 0E and the residue heated as in Example 1 for 20 hours at 160 C. Following this, it is possible either to distill off the trimethylaluminium immediately in vacuo or-after cooling-to extract as described under (a) above, in this case conveniently with pentane.

(c) In. the presence of the originally used hexane, heating is carried out under pressure and agitation at 160 C., and the whole worked up according to (a) and (b).

Example 3 The procedure of Example 1 or 2 is followed, but three kg. of ethyl chloride are used instead of the 4.8 kg. of ethyl bromide. In each case a pressure boiler suitable for use up to about atm. and furnished withv a pressure reflux condenser is employed, from the top of which the gases of the C2 series (ethylene, ethane), which accumulate in the vessel and cause a gradual inadmissible rise in pressure, are released from time to time. These gases are formed by secondary reactions. The whole further process is described in Example 1.

Example 4 In the conversion described in this example, of 552 g. of butyl iodide with 75 g. of aluminium-magnesium alloy, the final reaction mixture consists of 420 g. of magnesium iodide and 200 g. of tributylaluminium. From this disparity between solid phase and liquid, difliculties may arise, which may be avoided by the following procedure. A stout-walled, completely Welded, cylindrical, steel pot of about three litres content (diameter of base=height of cylinder) serves as the reaction vessel. The cylinder jacket carries a portion of steel tube welded in as neck. About 75 g. of the aluminium-magnesium alloy (40:60) is introduced into the pot, which has previously been flushed out with nitrogen. Furthermore a number of grinding pellets, consisting conveniently of pieces of 6- edged steel of 10-15 mm. diameter and cut to length=width are also introduced. The pot is mounted on a suitable rocking table and the neck connected with the necessary stationary fittings via a flexible metal tube.

Whilst shaking continuously, 550 g. of n-butyl iodide are admitted to the pot at a speed which maintains the reaction temperature at about C. Following this, the temperature is maintained at this level for some time and is then raised to C.

The tributylaluminium thus formed is easily extracted from the reaction mass by means of a hydrocarbon solvent (under nitrogen).

We claim:

1. Process for the production of aluminium trialkyls free from substantial quantities of halogen which comprises reacting an alkyl halide at a temperature between 30 and C. with a magnesium-aluminium alloy containing from 57 to 65% of magnesium and from 43 to 35% of aluminium in an ether-free reaction mixture and recovering the aluminium trialkyl thus formed.

2. Process according to claim 1, which comprises rcacting an alkyl halide in the presence of an inert solvent, with a magnesium-aluminium alloy.

3. Process acccording to claim 2, in which said reaction is elfected with a hydrocarbon as a solvent.

4. Process for the production of halogen-free aluminium trialkyl, which comprises reacting an alkyl halide at a temperature between 30 and 170 C. with a magnesium aluminium alloy containing from 5 7 to 65% of magnesium and from 43 to 35% of aluminium in an ether-free reaction mixture, and thereafter treating the aluminium trialkyl thus formed with a finely divided magnesium-aluminium alloy of the composition specified above.

References Cited in the file of this patent Wendt: Ber., vol. 56, pages 466-472 (1923). Reid et al.: Chem. Soc. Jour. (1948) pages 1597 to 1601.

Grosse et al.: J. Org. Chem, vol. 5, page 110. 

1. PROCESS FOR THE PRODUCTION OF ALUMINIUM TRIALKYLS FREE FROM SUBSTANTIAL QUANTITIES OF HALOGEN WHICH COMPRISES REACTING AN ALKYL HALIDE AT A TEMPERATURE BETWEEN 30 AND 170* C. WITH A MAGNESIUM-ALUMINIUM ALLOY CONTAINING FROM 57 TO 65% OF MAGNESIUM AND FROM 43 TO 35% OF ALUMINIUM IN AN ETHER-FREE REACTION MIXTURE AND RECOVERING THE ALUMINIUM TRIALKYLTHUS FORMED. 